Investigating the effect of delamination on self-diagnostic behavior of carbon/CNT epoxy composites

In this paper, the piezo-resistivity effect is utilized to experimentally investigate self-diagnostic behavior of composite laminates in determining delamination. In order to do so, composite laminated beams with unidirectional carbon fibers and epoxy resin containing CNT are produced while Teflon tape is placed between layers of some samples to artificially insert delamination. Three-point bending tests are conducted and stress-strain curves and electrical resistance of the samples are measured for not-damaged and damaged beams. The stress-strain curves are applied to interpret and determine damage mechanisms and to extract time data for the evolution of each damage mechanism. This time data is then used to determine the self-diagnostic behavior based on the variation of electrical resistance of the samples. The results show that in general, the electrical resistance of the not-damaged samples is higher than the damaged ones. This fact shows that piezo-resistivity effect can determine the existence of the delamination in the samples. Moreover, the propagation of delamination leads to electrical resistance increase when the delamination is placed far from the neutral axis of the beam. In addition, decreasing the dimension of the delamination reduces the sensitivity of the self-diagnosing behavior, which means that the variation of electrical resistance cannot determine the evolution of small sized delamination. On the other hand, the longitudinal location of delamination does not have a sensible effect on the behavior.